During the lifetime of a patient, it may be necessary to perform a joint replacement procedure on the patient as a result of, for example, disease or trauma. The joint replacement procedure may involve the use of a prosthesis which is implanted into one or more of the patient's bones. In the case of a patella replacement procedure, an orthopaedic prosthesis is implanted into the patient's patella. Specifically, a prosthetic patella implant component is secured to the patient's natural patella such that its posterior surface articulates with a femoral component during extension and flexion of the knee.
To facilitate the replacement of the articulating surface of the natural patella with the prosthetic patella, orthopaedic surgeons use a variety of orthopaedic surgical instruments such as, for example, saws, drills, mills or reamers to resect the posterior surface of the patella and then to prepare the resected surface for fixation of the prosthetic patella.
Common fixation elements for prosthetic patellae include one or more pegs extending out from the bone-facing (anterior) surface to be received in complementary recesses or holes drilled or reamed into the patella.
In some prosthetic patella implants, the articulating surface is dome-shaped, as in U.S. Pat. No. 5,593,450. In other types of prosthetic patella implants, the articulating surface has an asymmetric shape to be received and track within the patellar groove in the prosthetic femoral implant component. An example of such an asymmetrically-shaped prosthetic patella is disclosed in U.S. Pat. No. 6,074,425. With such asymmetric patella implants, rotational alignment of the implant impacts the way in which the patella implant tracks in the trochlear groove of the femoral implant. Such asymmetric patella implants typically include a plurality of pegs extending out from the anterior surface to be received in the complementary holes drilled in the patella surface. However, the surgeon typically cannot fully evaluate patellar tracking until trial patellar and femoral components are in place, which generally requires that the complementary holes be drilled before the trial is placed on the resected patella. If the surgeon determines that the patella trial does not track correctly, there is little opportunity to make adjustments since the mounting holes have already been drilled into the resected patella surface.